John Rodgers on sat 7 feb 98

I find myself needing to reduce/eliminate the drying time between
throwing and firing. Actually need to be able to throw and fire the same
day, at least, but preferrably off the wheel and into the fire. Has
anyone any experience in firing wet clay right off the wheel in a Raku
Kiln? Does the rapid heating simply cause the work to explode into a
zillion pieces because of the water going to steam so rapidly. Logic
suggests that it would explode, but would an open body - grog filled
clay reduce or stop that problem? Would reducing the heat input and
stretching out the firing time have any effect?

The key element for me in this is trying to get the whole process - from
throwing to completed firing - down to one day. Raku temps are ok. I'm
not after vitrification. Just want to make ornamental things with
students that can be completed in a single day.


Would appreciate any comments, suggestions, cautions, recommendation,
etc. And if this is old ground already covered, my apology to the list
membership for taking up the time and space.

TIA

John Rodgers
Trying to figure it out in Alabama

Sandra Jimison on mon 21 feb 11

Hi, My name is Sandra, I am new to clayart, or returning from many years aw=
ay.

I have just started doing raku on my own, though I have been to a few works=
hops over the years, this is my first at being the decision maker.

I fired my kiln last weekend. Everything was going fine until I got to the=
critical stage. My pots went from looking cold to bubbling. My initial t=
hought was this was the inital bubble, they would settle down, and be ready=
. I sat there and watched them for 10 minutes. I decided this was taking =
too long, so I shut her down.

I believe my pots look over fired. Why did this happen so fast?
Thanks for your help.

Sandra Jimison

WJ Seidl on mon 21 feb 11

Sandra:
The very first thing that comes to my mind is: "For what cone was that
clay?"
If you are using a "known" raku clay, then perhaps a further look...
Are there excessive amounts of organic materials in the clay that had to
burn out? (causing gas release and bubbling)
Was the glaze reacting to the clay body and bubbling as noted above?
What did the pyrometer say the temp inside the kiln was at the time you
noticed the bubbling?
Have you broken one of the pots and looked for carbon coring, indicating
overheating of the clay body? Is there any?
You mentioned "...went from looking cold to bubbling...". Please define
"cold"...not glowing red?
And perhaps a "stupid" question. Did the heat in the kiln increase so
rapidly that the clay (and / or glaze) didn't have sufficient time
to adjust to temp while still burning out the organics and trapped
moisture? As you mention, they do normally "settle down", but again, it
depends on the clay body and the glaze as to how long that should take.
Holding at top temperature for ten minutes might not have been long
enough for everything to settle down, or as you suspect, you may have
overfired. Again, what did the pyrometer say?

There are way too many variables in any raku firing to pin the cause of
"overfiring" on just one thing. It's usually a combination.
I believe you will find the answer somewhere in the questions I just
asked. There are many potters on the list that fire raku. I'm sure
some of them will have other questions for you.

Hope that helps,
Wayne Seidl


On 2/21/2011 7:35 AM, Sandra Jimison wrote:
> Hi, My name is Sandra, I am new to clayart, or returning from many years =
away.
>
> I have just started doing raku on my own, though I have been to a few wor=
kshops over the years, this is my first at being the decision maker.
>
> I fired my kiln last weekend. Everything was going fine until I got to t=
he critical stage. My pots went from looking cold to bubbling. My initial=
thought was this was the inital bubble, they would settle down, and be rea=
dy. I sat there and watched them for 10 minutes. I decided this was takin=
g too long, so I shut her down.
>
> I believe my pots look over fired. Why did this happen so fast?
> Thanks for your help.
>
> Sandra Jimison
>
>

Pottery by John on tue 22 feb 11

Sandra,

Perhaps you could give us the name of the clay, the recipe or name of the
glaze you were using, and how long you took to go from ambient temperature
to the glaze boiling on the pot, in addition to the information asked by
Wayne. Any observations you made about the kiln and the condition of the
exhaust (flames, clear, black etc.), assuming gas fired not electric, from
the flue may be helpful. Were flames touching the pots inside the kiln at
all?

John Lowes
Sandy Springs, Georgia
http://wynhillpottery.weebly.com/

Sandra Jimison on wed 23 feb 11

Okay,
I appreciate the resposes and questions.
The clay body I am using is from Kickwheel and is a cone 5-6 true raku clay=
.
The primary glaze is a dry mixed laguna white crackle raku.
The secondary glaze is straight copper carbonate simply mixed with water.
The third was simply a pre-mixed low fire Spectrum glaze.

Generally speaking the copper carb was good. Where it was on the bare pot =
it went generally matte. Where it was on top of the laguna glaze, I got so=
me good color.

Where the laguna glaze was alone... inside the pot it actually looked like =
it crawled judging by the way it seperated. On the outside of the pot, dep=
ending on the pot, it was good, or white with black polka dots. The top edg=
e of the pot bubbled.

The Spectrum glaze was good on the outside, but bubbled on the inside of th=
e pot.

I did not use a pyrometer, partly because I had fried mine. I do have a fr=
iend locally who buys up old studios and he is going to supply me with a re=
placement so I will have it next time.

As far as fuel and timing go:
I am using propane. My kiln is fiber on a brick base.
Timing:1st firing with preheating the base took 1hour 5min.
2nd load: 50 min, 3rd load: 1 hour

Here is the catch. because my kiln is fairly tall (3 feet), The first load=
I tried to do two lavers. After watching this for a while, it appeared un=
der the shelf was getting good and hot though the top shelf nothing was rea=
lly happening. The pots in the first load on the bottom shelf actually did=
pretty well.

Soo, for the second load I put the pots that were on the top shelf down, p=
ut the top shelf back on and left it empty.

The third load I did the same thing.

As far a breaking a pot to see if there is carbon coring goes, I wouldn't k=
now caron coring if it bit me in the a...

Thanks,

Sandra

Sandra Jimison on wed 23 feb 11

Okay,
I appreciate the resposes and questions.
The clay body I am using is from Kickwheel and is a cone 5-6 true raku cla=
y.
The primary glaze is a dry mixed laguna white crackle raku.
The secondary glaze is straight copper carbonate simply mixed with water.
The third was simply a pre-mixed low fire Spectrum glaze.

Generally speaking the copper carb was good. Where it was on the bare pot =
it went generally matte. Where it was on top of the laguna glaze, I got so=
me good color.

Where the laguna glaze was alone... inside the pot it actually looked like =
it crawled judging by the way it seperated. On the outside of the pot, dep=
ending on the pot, it was good, or white with black polka dots.

The spectrum glaze was good on the outside, but bubbled on the inside of th=
e pot.

I did not use a pyrometer, partly because I had fried mine. I do have a fr=
iend locally who buys up old studios and he is going to supply me with a re=
placement so I will have it next time.

As far as fuel and timing go:
I am using propane. My kiln is fiber on a brick base.
Timing:1st firing with preheating the base took 1hour 5min.

Les on wed 23 feb 11

Hi Sandra - if you were using a pyrometer, what temperature do you fire =
=3D
to?

Les Crimp on Vancouver Island.
lcrimp@shaw.ca

On 2011-02-23, at 12:26 PM, Sandra Jimison wrote:

> Okay,
> I appreciate the resposes and questions.
> The clay body I am using is from Kickwheel and is a cone 5-6 true =3D
raku clay.
> The primary glaze is a dry mixed laguna white crackle raku.
> The secondary glaze is straight copper carbonate simply mixed with =3D
water.
> The third was simply a pre-mixed low fire Spectrum glaze.
>=3D20
> Generally speaking the copper carb was good. Where it was on the bare =
=3D
pot it went generally matte. Where it was on top of the laguna glaze, I =
=3D
got some good color.
>=3D20
> Where the laguna glaze was alone... inside the pot it actually looked =3D
like it crawled judging by the way it seperated. On the outside of the =3D
pot, depending on the pot, it was good, or white with black polka dots.
>=3D20
> The spectrum glaze was good on the outside, but bubbled on the inside =3D
of the pot.
>=3D20
> I did not use a pyrometer, partly because I had fried mine. I do have =
=3D
a friend locally who buys up old studios and he is going to supply me =3D
with a replacement so I will have it next time.
>=3D20
> As far as fuel and timing go:
> I am using propane. My kiln is fiber on a brick base.
> Timing:1st firing with preheating the base took 1hour 5min.

Pottery by John on wed 23 feb 11

Good clay body for raku, I use this one myself, so no problem I see there.
The times to fire look reasonable for raku, in fact a little slower than I
go typically. Since I got a pyrometer to supplement my eyeball approach I
can go up quicker without overshooting.

Laguna inside the pot. I occasionally get crawling inside because I pour
the inside and sometimes the glaze gets too thick before I get it out.

The Spectrum may have underfired on the inside and never smoothed out, or
maybe it had a reducing atmosphere inside it didn't care for.

My best guesses. Doesn't help much, but may give you some ideas.

John Lowes
Sandy Springs, Georgia
http://wynhillpottery.weebly.com/


----- Original Message -----
From: "Sandra Jimison"
To:
Sent: Wednesday, February 23, 2011 3:47 PM
Subject: raku firing


> Okay,
> I appreciate the resposes and questions.
> The clay body I am using is from Kickwheel and is a cone 5-6 true raku
> clay.
> The primary glaze is a dry mixed laguna white crackle raku.
> The secondary glaze is straight copper carbonate simply mixed with water.
> The third was simply a pre-mixed low fire Spectrum glaze.
>
> Generally speaking the copper carb was good. Where it was on the bare po=
t
> it went generally matte. Where it was on top of the laguna glaze, I got
> some good color.
>
> Where the laguna glaze was alone... inside the pot it actually looked lik=
e
> it crawled judging by the way it seperated. On the outside of the pot,
> depending on the pot, it was good, or white with black polka dots. The to=
p
> edge of the pot bubbled.
>
> The Spectrum glaze was good on the outside, but bubbled on the inside of
> the pot.
>
> I did not use a pyrometer, partly because I had fried mine. I do have a
> friend locally who buys up old studios and he is going to supply me with =
a
> replacement so I will have it next time.
>
> As far as fuel and timing go:
> I am using propane. My kiln is fiber on a brick base.
> Timing:1st firing with preheating the base took 1hour 5min.
> 2nd load: 50 min, 3rd load: 1 hour
>
> Here is the catch. because my kiln is fairly tall (3 feet), The first
> load I tried to do two lavers. After watching this for a while, it
> appeared under the shelf was getting good and hot though the top shelf
> nothing was really happening. The pots in the first load on the bottom
> shelf actually did pretty well.
>
> Soo, for the second load I put the pots that were on the top shelf down,
> put the top shelf back on and left it empty.
>
> The third load I did the same thing.
>
> As far a breaking a pot to see if there is carbon coring goes, I wouldn't
> know caron coring if it bit me in the a...
>
> Thanks,
>
> Sandra

Snail Scott on wed 23 feb 11

On Feb 23, 2011, at 2:47 PM, Sandra Jimison wrote:
> ...The Spectrum glaze was good on the outside, but bubbled on the =3D
inside of the pot...

This is nearly always a sign of underfiring, as=3D20
the outside of any form heats ahead of the inside.
Many glazes (raku and otherwise) go through a=3D20
phase near maturity in which they bubble, since the=3D20
there is still outgassing, and the gas must escape
the now-liquid glaze layer. When the bubbles stop,=3D20
it's often a good visual cue that the firing is nearly
done. It's also common for some part of the shape=3D20
that's less visible (an interior, or the side furthest=3D20
from the flame path) to still have unseen bubbles.=3D20
Take this as a sign to fire a bit hotter/longer next=3D20
time, and the bubble problem should resolve.

-Snail


>=3D20
> I did not use a pyrometer, partly because I had fried mine. I do have =
=3D
a friend locally who buys up old studios and he is going to supply me =3D
with a replacement so I will have it next time.
>=3D20
> As far as fuel and timing go:
> I am using propane. My kiln is fiber on a brick base.
> Timing:1st firing with preheating the base took 1hour 5min.
> 2nd load: 50 min, 3rd load: 1 hour
>=3D20
> Here is the catch. because my kiln is fairly tall (3 feet), The first =
=3D
load I tried to do two lavers. After watching this for a while, it =3D
appeared under the shelf was getting good and hot though the top shelf =3D
nothing was really happening. The pots in the first load on the bottom =3D
shelf actually did pretty well.
>=3D20
> Soo, for the second load I put the pots that were on the top shelf =3D
down, put the top shelf back on and left it empty.
>=3D20
> The third load I did the same thing.
>=3D20
> As far a breaking a pot to see if there is carbon coring goes, I =3D
wouldn't know caron coring if it bit me in the a...
>=3D20
> Thanks,
>=3D20
> Sandra

Steve Mills on thu 24 feb 11

My two-penny-worth.=3D20
Over the years I've done a lot of Raku-process firing educationally and pri=
v=3D
ately, and have found that using a Pyrometer and Thermocouple is counter-pr=
o=3D
ductive.=3D20
Watching the glazes go through their cycle of sintering, gassing, and final=
l=3D
y maturing and looking like syrup is far more reliable. After all your "Eye=
"=3D
is your most trustworthy piece of equipment isn't it, and it improves with=
u=3D
se!

Steve M


Steve Mills
Bath
UK
www.mudslinger.me.uk
Sent from my Ipod touch

On 23 Feb 2011, at 22:48, Les wrote:

> Hi Sandra - if you were using a pyrometer, what temperature do you fire =
t=3D
o?
>=3D20
> Les Crimp on Vancouver Island.
> lcrimp@shaw.ca
>=3D20
> On 2011-02-23, at 12:26 PM, Sandra Jimison wrote:
>=3D20
>> Okay,
>> I appreciate the resposes and questions.
>> The clay body I am using is from Kickwheel and is a cone 5-6 true raku =
c=3D
lay.
>> The primary glaze is a dry mixed laguna white crackle raku.
>> The secondary glaze is straight copper carbonate simply mixed with water=
.=3D

>> The third was simply a pre-mixed low fire Spectrum glaze.
>>=3D20
>> Generally speaking the copper carb was good. Where it was on the bare p=
o=3D
t it went generally matte. Where it was on top of the laguna glaze, I got =
s=3D
ome good color.
>>=3D20
>> Where the laguna glaze was alone... inside the pot it actually looked li=
k=3D
e it crawled judging by the way it seperated. On the outside of the pot, d=
e=3D
pending on the pot, it was good, or white with black polka dots.
>>=3D20
>> The spectrum glaze was good on the outside, but bubbled on the inside of=
t=3D
he pot.
>>=3D20
>> I did not use a pyrometer, partly because I had fried mine. I do have a=
f=3D
riend locally who buys up old studios and he is going to supply me with a r=
e=3D
placement so I will have it next time.
>>=3D20
>> As far as fuel and timing go:
>> I am using propane. My kiln is fiber on a brick base.
>> Timing:1st firing with preheating the base took 1hour 5min.